The Histopathology Shared Resource began operations in October 1999 to provide a full-range of histopathology and histotechnology services in support of research activities at AECCC with a focus on mouse models. The need for this facility grew rapidly over the last funding period with the expansion of mouse models developed in the Transgenic and Gene Targeting Shared Resources. The facility director, Dr. Robert Russell, is a board-certified veterinary pathologist with 16 years of experience in biomedical animal model research, recruited to AECCC in January 1999 to develop this service. New laboratory space was committed for this facility that was increased in May 2000 as demand for services rapidly increased. By July 2000, 54 AECCC investigators had utilized the facility with 60 submissions per month. Services provided include: fixation, tissue processing and paraffin embedding for sectioning, routine hematoxylin and eosin and special stains, preparation of unstained slides for immunohistochemistry and in situ hybridization, and cryostat sectioning for frozen sections. The facility provides training, protocols, and assistance for investigators in the conduct of these and other procedures. Pathology services are provided to characterize morphologic and other phenotypic evaluations in transgenic and gene-targeted mice. Pathology examinations include gross necropsy, animal and organ weights of representative mice, complete and intensive histologic evaluation of adult mice or embryos. The facility also provides documentation and other assistance for publications. Consultation is available to investigators for specimen preparation and histologic localization of gene expression markers (e.g. immunostaining, galactosidase). The facility has the capability, in-house, to assist with, and develop, other specialized tests and procedures. The facility identifies resources to meet particular needs of AECCC investigators and provides equipment, software and relevant training. This includes a Zeiss Axioskop 2 brightfield microscope with Optronics digital camera and Image Pro software for image analysis. Additional comparative pathology services and tests are conducted on genetically engineered mice as warranted. These include x-rays, hematology, and clinical chemistry. This facility interacts closely with the Animal Barrier Shared Resources to identify diseases in the animal population and to support the husbandry and management of genetically engineered mice used in cancer research. This protects the integrity of the mouse colony and assures that phenotypic analyses are not confounded by concurrent viral and bacterial diseases. Facility charges are 30-50% lower than commercial laboratories, and may be even lower when compared to costs of medical histology services.